This invention relates primarily to pore forming in metal bodies, and in particular to methods of producing microporous bodies of tungsten.
In the development of thermionic reactors where the emitter contains a fissile fuel material, the generation of fission product gases becomes a problem. The emitter body, which is spaced apart from the collector by a very narrow gap, tends to enlarge and change dimensionally in reaction to the increase in the internal gas pressure due to the generation of fission product gases. The enlargement of the emitter, if left unchecked, will, in a time shorter than the life of the fissile fuel, cause the emitter to come in contact with the collector, thus shorting out the converter cell and reducing the power generating capacity of the thermionic reactor.
Venting of the emitter must be achieved without releasing any particles of fissile fuel which would detrimentally contaminate the emitter surface, collector surface, or cesium vapor, or detrimentally increase the space charge effect.
The present invention concerns a process for forming porous openings in tungsten used as cladding for the emitter in thermionic converter containing fissile fuel, which acts somewhat in the manner of a filter to permit the flow of fission product gases, but prevents the release of fissile fuel particles outside the emitter cladding. To be effective, such pore openings and passageways must be microscopic in size, e.g., the pore openings must be large enough to permit the molecules and atoms of the fission product gases to pass through, but small enough to retain the fissile fuel molecules and particles.